Biology I - GENETICS
1-12 Novak
Gregor Mendel
1822-1884
MENDEL’S PRINCIPLES
I. ALLELES
• Any organism has two units of heredity (genes) for each trait in every body cell
II. SEGREGATION
• The two units (genes) for a trait are separated in the cell; one gene is found on a chromosome while the other is located in the same place on its partner (homologous) chromosome
III. DOMINANCE• A. When two genes of a trait are different in the cells of
the organism, the gene that shows up is the dominant while the gene that remains hidden is the recessive
• B. Combinations of the two genes (genotypes)1. Homozygous (pure) dominant - both genes are dominant2. Homozygous (pure) recessive - both genes are recessive3. Heterozygous (hybrid) - one gene is dominant & the
other is recessive
IV. RECOMBINATION - (INDEPENDENT ASSORTMENT)
• In each new generation there is a complete new rearrangement of the units of heredity (genes)
Following the GenerationsFollowing the Generations
Cross 2 Cross 2 Pure Pure
PlantsPlantsTT x ttTT x tt
Results Results in all in all
HybridsHybridsTtTt
Cross 2 Cross 2 HybridsHybrids
getget3 Tall & 1 3 Tall & 1
ShortShortTT, Tt, ttTT, Tt, tt
Generation “Gap”Generation “Gap”• Parental PParental P11 Generation Generation = the parental generation in a breeding experiment= the parental generation in a breeding experiment..• FF11 generation generation = the first-generation offspring in a breeding experiment. = the first-generation offspring in a breeding experiment.
(1st filial generation)(1st filial generation)– From breeding individuals from the PFrom breeding individuals from the P11 generation generation
• FF22 generation generation = the second-generation offspring in a breeding experiment. = the second-generation offspring in a breeding experiment.
(2nd filial generation)(2nd filial generation)– From breeding individuals from the FFrom breeding individuals from the F11 generation generation
Mendel’s Experimental Mendel’s Experimental ResultsResults
Thomas Hunt Morgan
1866-1945
Incomplete Dominance Incomplete Dominance (blending inheritance)(blending inheritance)
• INCOMPLETE DOMINANCE
• A condition in which both alleles for a characteristic are partially expressed
Incomplete DominanceIncomplete Dominance• F1 hybrids F1 hybrids have an appearance somewhat in betweenin between or a blend of the
phenotypes phenotypes of the two parental varieties.• Example:Example: snapdragons (flower)snapdragons (flower)• red (RR) x white (WW)
• R = red flowerR = red flower• W = white flower
W
W
R R
Incomplete DominanceIncomplete Dominance
RWRW
RWRW
RWRW
RWRW
RR RR
All RW =All RW = pink pink(heterozygous pink)(heterozygous pink)
produces theproduces theFF11 generation generation
W
W
Incomplete DominanceIncomplete Dominance
• CODOMINANCE
• A condition in which both alleles for a characteristic are fully expressed
Codominant white and pink
Codominant white and pink
Homozygous Red
Hereford Red
Homozygous white
Roan hybrid
Roan hybrid
Codominant cross
Sex-Linked Inheritance
Color Blindness
normal - trichromatic color vision protanopia red-green blindness (no red cones) deutanopia red-green blindness (no green cones) tritanopia blue-yellow blindness (no blue cones) typical achromatopsia (no cones; rod monochromat) protanomaly (anomalous red cones) deutanomaly (anomalous green cones) tritanomaly (anomalous blue cones)
atypical achromatopsia (low cones; cone monochromat)
TYPES OF COLOR BLINDNESS
Red Green Color BlindnessMale1.01%Female0.02%
Sex-linked TraitsSex-linked Traits• Traits (genes) located on the Traits (genes) located on the sex chromosomessex chromosomes• Sex chromosomes are Sex chromosomes are X and YX and Y• XXXX genotype for females genotype for females• XYXY genotype for males genotype for males• Many Many sex-linked traitssex-linked traits carried on carried on XX chromosome chromosome
Hemophilia
Female CarriersFemale Carriers
The effects of hemophilia
Human BloodCoagulationCascade
DIHYBRID INHERITANCE
Pea Plants
Tall = TT, TtShort = tt
Height Seed Color
Yellow = YY, YyGreen = yy
Let’s cross a homozygous tall (TT), homozygous yellow seed (YY) plant with a short (tt), green seed (yy) plant.
TTYY x ttyy
These are the genotypes of the two plants.
Independent Assortment
Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants).
TTYY
TY
First T with first Y
Gamete 1 = sperm, egg, pollen . . .
Independent Assortment
Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants).
TTYY
TY TY
First T with second Y
Gamete 1 Gamete 2
Independent Assortment
Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants).
TTYY
TY TY TY
Second T with first Y
Gamete 1 Gamete 2 Gamete 3
Independent Assortment
Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants).
TTYY
TY TY TY YT
Second T with second Y
Gamete 1 Gamete 2 Gamete 3 Gamete 4
Dihybrid Punnett Square - F1
TY TY TY TY
ty
ty
ty
ty
P1 = TTYY
P2 = ttyy Will be F1 Generation
Dihybrid Punnett Square - F1
TY TY TY TY
ty TTYy
ty TTYy
ty TTYy
ty TTYy
Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TTYY TtYY TtYY TTYY
ty TTYY TTYY TTYY TTYY
ty TTYY TTYY TTYY TTYY
Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
Dihybrid Punnett Square - F1
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
Genotype ratio:TtYy - 16/16
Phenotype ratio:Tall, Yellow - 16/16
Dihybrid Punnett Square – F2We need to pair up the genes which can be given to each
gamete (egg and pollen).Let’s cross two of the plants from the F1 generation
TY TY TY TY
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
ty TtYy TtYy TtYy TtYy
x
.
TY Ty t Y yt
We need to pair up the genes
Dihybrid Punnett Square F2
TY Ty tY ty
TY
Ty
tY
ty
Both the plants can give the same gene combinations to their gametes, so the pairs along the top and down the side are the same.
Dihybrid Punnett Square – F2
When you pair up the gametes from the two plants, always put like letters together and within the like letters, put the CAPITAL letter in front of the lowercase letter.
Dihybrid Punnett Square F2
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty ???? ???? ???? ????
tY ???? ???? ???? ????
ty ???? ???? ???? ????
Your Turn!!
Dihybrid Punnett Square F2
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty TTYy TTyy TtYy Ttyy
tY TtYY TtYy ttYY ttYy
ty TtYy Ttyy ttYy ttyy
F2 generation
Dihybrid Punnett Square F2
TY Ty tY ty
TY TTYY TTYy TtYY TtYy
Ty TTYy TTyy TtYy Ttyy
tY TtYY TtYy ttYY ttYy
ty TtYy Ttyy ttYy ttyy
Genotype and phenotype ratios?
F2 Genotype RatioTTYY - 1TTYy - 2TtYY - 2TtYy - 4TTyy - 1Ttyy - 2ttYY - 1ttYy - 2ttyy - 1
F2 Phenotype RatioTTYY - 1TTYy - 2TtYY - 2TtYy - 4TTyy - 1Ttyy - 2ttYY - 1ttYy - 2ttyy - 1
Tall, Yellow - 9
Tall, Green - 3
Short, Yellow - 3
Short, Green - 1
Another Mendelian Dihybrid Problem
Dihybrid F2 Results
Dihybrid F2 Results
•The End